Separation of 2, 6-xylenols from cresols



2,789,146 SEPARATION OF 2,6-XYLENOLS FROM CPEfiGLS Martin B. Neuworth, Pittsburgh, Pa., assigor to Pittsburgh Consolidation Coal Company, Pittsburgh, Pa, a corporation of Pennsylvania Application August 10, 1954, Serial No. 448,?48 6 Claims. (Cl. 260-627) The present invention relates to the separation of 2,6- xylenol from cresols, and more particularly, to a double solvent extraction process for removing 2,6-xylenol from a distillate fraction of cresols.

2,6-xylenol is a naturally occuring phenol amounting to as much as 20% of the cresol distillate derived from low temperature carbonization of bituminous coal. It also occurs in petroleum cresylics, in coke oven tars, oil shale distillates, coal hydrogenation oils and the like. Its boiling temperature is above that of ortho-cresol and below that of meta and para-cresol. Accordingly it is concentrated in what is normally termed the cresol distillate whence it cannot be removed readily by ordinary distillation techniques. (See for example British Patent 708,925, published May 12, 1954). Thus 2,6-xylenol appears as a contaminant in cresol distillate fractions. Because 2,6-xylenol is not a gel-forming tar acid, its presence in the cresol distillates diminishes their value as a starting material for resin production. By itself, however, 2,6- xylenol is a valuable material for use in anti-oxidants, plasticizers and the like.

2,6-xylen-ol also presents a problem in the recovery of products of the cracking and isomerization of phenols and mixtures thereof. For example, the isomerization of ortho-cresol produces significant quantities of 2,6-xy1enol through a disproportionation reaction. The isomate contains 2,6-xylenol in mixture with meta and para-cresol products and unreacted ortho-cresol.

I have discovered a method for recovering 2,6-xylenol from cresol distillates by a double solvent extraction technique employing aqueous methanol as a polar solvent and a low boiling paraifinic naphtha fraction as a nonpolar solvent. In the preferred embodiment of this invention, the extraction process is carried out countercurrently in a center feed extraction system. The 2,6-xylenol is selectively dissolved in the nonpolar solvent while the cresols are selectively dissolved in the polar solvent.

In U. S. Patent 2,666,796, a double solvent extraction process is described for separating phenols and neutral oils contained in tar acid oil. in that process tar acid oil is contacted under solvent extracting conditions with parafiinic naphtha and aqueous methanol as solvents. The phenols are selectively recovered in the aqueous methanol solvent and the neutral oils selectively recovered in the naphtha solvent. The aqueous methanol solvent has a concentration range of 55 to 75% by weight of methanol. According to the above mentioned patent, 2,6-xyleno1 in the tar acid oil is recovered along with other phenols in the aqueous methanol phase. I now find that by employing a 30 to 50 weight percent aqueous methanol solution and a paralfinic naphtha fraction as solvents, 2,6-xylenol can be recovered in the naphtha phase, from a feed stock consisting essentially of phenols which are substantially free of neutral oils.

The nonpolar solvent of this invention should be essentially parafiinic in character. Such solvents may be obtained from the distillation of parafinic petroleum stocks. ts boiling range should be 60 to 120 C. but preferably 60 to 100 C. in order to simplify the subsequent separation of the naphtha extract by distillation. The naphtha density should be less than 0.80 and preferably less than tilted dtates hatent ice 0.75 to insure sufiicient gravity difference between the two phases in the extraction column to effect a ready separation of the phases. The hexane cut of paraffinic naphtha combines all these critical properties and accordingly is preferred as the nonpolar solvent in this invention.

The polar solvent, aqueous methanol, should contain 30-50% by weight of methanol. So long as the cresol feedstock is essentially uncontaminated with neutral oils no emulsification problems arise. In concentrations exceeding about 50 weight percent methanol, the purity of the 2,6-xylenol recovered in the hexane phase decreases sharply. With aqueous methanol solutions having concentrations less than about 30%, the recovery of 2,6-xylen'ol diminishes.

The process of this invention may be practiced with either the naphtha or the aqueous methanol solution as the continuous phase in the phase contacting portion of the extraction column.

Fora better understanding of my invention, its objects and advantages, reference should be had to the following description and accompanying drawing which is a diagrammatic illustration of the preferred embodiment of the apparatus adapted tothe practice of this invention.

Referring to the drawing a cresol distillate containing cresols and 2,6-xylenol is pumped from a storage tank 10 continuously through a pipeline 12 into a continuous, countercurrent, double solvent center feed extraction column 14. The extraction column may be of any convenient design capable of providing a sufhcient number of theoretical extraction stages to effect the desired separation of 2,6-xy1en'ol. A conventional packed tower may be used, for example, as well as a pierced plate column, a bubble plate column or a column containing alternate Zones of quiescence and turbulence.

e cresol feed should be essentially free of neutral oils, tar bases, sulfur compounds and other contaminants. Small quantities of neutral oils and sulfur compounds may be present (up to about 5%). These are recovered in the naphtha solvent where they contaminate the 2,6-xylenoh The preferred feedstock is the cresol distillate fraction of phenols consisting essentially of cresols and 2,6-xylenol. A distillate fraction of phenols having an atmospheric boiling range of about to 205 C. combines these properties, i. c. it contains all the 2.,6-xylenol and essentially all the cresol in the crude tar acid source. Frequently small quantities (e. g. a few percent) of other phenols may occur in this fraction, for example, phenol and some of the other xylenol isomers. The presence of phenols other than cresols and 2,6-xylenol, however, does not alter the effectiveness of the present process.

Aqueous methanol solvent is fed continuously from the aqueous methanol storage tank 16 through a conduit 18 into the top of the extraction column 14. Naphtha solvent is sent continuously from the naphtha storage tank 20 through a pipeline 22 into the base of the extraction column 14.

Since the density of the aqueous methanol solvent exceeds the density of the naphtha solvent, the aqueous methanol descends through the column dissolving the cresols in the .feed, while the lighter naphtha solvent passes countercurrently upward through the column dissolving 2,6-xylenol. Trace quantities of neutral oils and sulfur compounds from the feedstock will be recovered in the naphtha phase along with the 2,6-xylenol.

In the preferred embodiment, the feedstock is introduced into the center of a vertical, countercurrent extraction column. In some instances, the feedstock might be mixed with one of the two solvents to permit the use of end-feed columns.

For every volume of phenols fed to the extraction column, from 1.0 to 15.0 volumes of aqueous methanol S and from 1.0 to 15.0 volumes of naphtha should be employed. Aqueous methanol extract, containing phenols freed of 2,6-xylenol, is recovered from the bottom of column 14 through conduit 24 and sent into a stripping column 26 for separation of the extract and the solvent. Methanol is recovered overhead through conduit 30 and returned to the methanol storage tank 16 for recycle. A condenser and refluxing system may be installed in the conduit 30. Water, together with the phenols freed of 2,6-xylenol, is recovered from the base of the stripping column 26 through conduit 28. If desired a cooling condenser may be inserted in the conduit 28. The water is separated from the extracted phenols by phase separation in a decanter 40 and returned through conduit 42 to the aqueous methanol storage tank 16 for recycle. Additional methanol can be added to the solvent circulation system through conduit 44 to compensate for solvent losses in the system.

The naphtha solution containing 2,6-xylenol is recovered from the top of the extraction column 14 through a conduit 32 and sent to a naphtha stripping column 34. The naphtha solvent is recovered overhead through conduit 36 and returned to the naphtha storage tank 20 for recycle. If desired, a condenser and refluxing system may be inserted in conduit 36. 2,6-xylenol is recovered from the bottom of the stripping column 34 through the conduit 38. A cooling condenser may be inserted in the conduit 38.

The extraction process is preferably operated at atmos- V pheric pressures and temperatures.

To illustrate the present process, tar. from low temperature carbonization of bituminous coal was fractionated by distillation to produce a distillate boiling from 180 to 230 C. This fraction, containing all the phenol, cresol and xylenol in the tar, together with neutral oils, was processed in accordance with U. S. Patent 2,666,796 (abovementioned) to recover the phenols free of neutral oils. Upon precise fractionation, the distillate fraction boiling from 190 to 203 C. had the following analysis:

Percent o-Cresol 38 m-Cresol 25 p-Cresol 18 2,6-xylenol 18 Thus the 2,6-xylenol contained in the tar acid oil remains with the phenol extract produced in the double- Run A B O Aqueous Methanol Concentration, Wt.

Percent 45 45 35 Solvent/Feed Ratio, vol./vol.:

Aqueous Methanol 1 2 5 10 N aptha 0 10 5 Feed Composition, Wt. Percent:

o-cresol 12. 2 43. 0 42. 2 m-cresol- 28.0 24. 0 28. 6 g-screspeL i3. 9 16. 0 13. 9

, -xy n 5. 3 17.0 15. 3

Naptha Extract:

Wt. Percent of Feed-.- 14. 8 16. 1 9. 1 2,6-xy1enol 59. 2 67. 3 91. 2 o-cresol 24. 1 19. 1 8. 8 m,p-cresol 16. 7 13. 6

Aqueous Methanol Extract:

, Wt. Percent of Feed 85.2 83. 9 90. 9 2,6-xylenol 6. 8 6. 8 6. l o-cresol 44. 1 40. 5 44. 0 m,p-cresol 49. 1 52. 7 48. 8

Recovery, 2,6-xylenol, Wt. Percent 60. 3 65. 5 60. 0

The feedstock in the three runs of Table I contained from 15.3 to 17.0 wt. percent 2,6-xylenol. This concentration of 2,6-xylenol was reduced to 6.1 to 6.8 wt. percent of the product cresol fraction. The 2,6-xylenol was recovered in purities ranging from 59.2 to 91.2% by Weight. It is of interest to note that the azeotropic distillation technique described in British Patent 708,925 (above-mentioned) increased the concentration of 2,6- xylenol from an initial level of 5% to a final value of only 22 to 30%.

From 60.0 to 65.5 wt. percent of the 2,6-xylenol in the feed tar acids was removed and recovered. The naphtha-to-feed ratio ranged from 5-10 parts by volume; the aqueous methanol to feed ratio ranged from 2 to 10 parts by volume. 7

The purity of cresol in the feedstock ranged from 83 to 84.7% by weight. The purity of the recovered cresols ranged from 93.2 to 93.9% by weight. By proper'adjustment of the solvent-to-feed flow rates, the purity and recovery of the cresol can be regulated. Improving the stage efiiciency of the extraction column results in improved purity and recovery.

Recovery of higher purity fractions of 2,6-xylenol can be accomplished by treating the naphtha extract through fractional crystallization.

According to the provisions of the patent statutes I have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

1 claim:

1. The method for separating 2,6-xylenol from a mixture consisting essentially of cresol and 2,6-xylenol which comprises introducing said mixture into a vertical, countercurrent extraction zone, introducing parafiinic naphtha solvent boiling in the range of 60-130 C. and having a density less than 0.8 into the bottom of said extraction zone, introducing an aqueous methanol solution containing 30-50 wt. percent of methanol into the top of said extraction zone, recovering from the bottom of said ex traction zone an aqueous methanol extract containing cresols and recovering from the top of said extraction zone a naphtha extract containing 2,6-xylenol.

2. The method for separating 2,6-xylenol from a cresol distillate fraction consisting essentially of phenols including 2,6-xylenol which comprising introducing said distillate fraction between the ends of a vertical, countercurrent extraction zone, introducing 1 to 15 volumes of parafi'inic naphtha solvent boiling in the range of 60 to C. and having a density of less than 0.8 into the bottom of said extraction zone, introducing 1 to 15 volumes of aqueous methanol solution containing 30-50 wt. percent methanol into the top of said extraction zone, recovering from the bottom of said extraction zone an aqueous methanol extract containing cresols and recovering from the top of said extraction zone a naphtha extract containing 2,6-xylenol.

3. The method for separating 2,6-xylenol from a distillate fraction consisting essentially of phenols including 2,6-xylenol boiling in the range of -205 C. which comprises introducing said distillate fraction between the ends of a vertical, countercurrent extraction zone, introducing 1 to 15 volumes of paraffinic naphtha solvent boiling in the range of 60130 C. and having a density of less than 0.8 into the bottom of said extraction zone, introducing 1 to 15 volumes of aqueous methanol solution containing 30-50 Wt. percent methanol into the top of said extraction zone, recovering from the bottom of said extraction zone an aqueous methanol extract containing phenols and recovering from the top of said extraction zone a naphtha extract containing 2,6-xylenol.

4. The method of claim 3 in which the paraffinic References Cited inthe file of this patent naphtha solvent is the continuous phase in the extraction UNITED STATES PATENTS zone.

s. The method of claim 3 in which the paraifinic 222 2 W etal 11512, 1951 naphtha solvent is the hexane distillate fraction of pe- 5 om et 1954 troleum naphtha. FOREIGN PATENTS 6. The method of 01mm 3 m whlch the paraflimc 708,925 Great Britain May 12 1954 naphtha solvent has a boiling range of 60-100 C. 

1. THE METHOD FOR SEPARATING 2,6-XYLENOL FROM A MIXTURE CONSISTING ESSENTIALLY FO CRESOL AND 2,6-XYLENOL WHICH COMPRISES INTRODUCING SAID MIXTURE INTO A VERTICAL, COUNTERCURRENT EXTRACTION ZONE, INTRODUCING PARAFFINIC NAPHTHA SOLVENT BOILING IN THE RANGE OF 60-130*C. AND HAVING A DENSITY LESS THAN 0.8 INTO THE BOTTOM OF SAID EXTRACTION ZONE, INTRODUCING AN AQUEOUS METHANOL SOLUTION CONTAINING 30-50WT. PERCENT OF METHONOL INTO THE TOP OF SAID EXTRACTION ZONE, RECOVERING FROM THE BOTTOM OF SAID EXTRACTION ZONE AN AQUEOUS METHANOL EXTRACT CONTAINING CRESOLS AND RECOVERING FROM THE TOP OF SAID EXTRACTION ZONE A NAPHTHA EXTRACT CONTAINING 2,6-XYLENOL. 